1. Technical Field
The present invention relates to a generator core including a yoke and magnetic pole portions.
2. Background Art
Power generating systems that utilize natural energy such as aerogenerator systems and hydrogenerator systems have been drawing attention in recent years. In particular, permanent-magnet generators for aero-power generation are used in many small aerogenerator systems such as mini aerogenerator systems with an output of several kilowatts and micro aerogenerator systems with an output of 1 kW or less. Unlike induction generators, the permanent-magnet generators do not need a power supply to a field winding, and therefore are expected to be utilized in isolated islands and mountain areas as independent power supply facilities. In addition, recently, the permanent-magnet generators have increasingly been installed in parks and on building rooftops in urban areas. However, such small aerogenerator systems require 100 to 200 times power generation costs of large power generating systems. Therefore, cost reduction of power generation is demanded in the field of small aerogenerator systems.
In many cases, the small aerogenerator systems are used as independent power sources. The power generated by a three-phase generator is converted into DC power through a full-wave rectifier and then is utilized either directly or after being accumulated in a battery. The DC power may also be used after frequency conversion via an inverter. Therefore, for better performance of the small aerogenerators, it is necessary to increase the amount of generated power by uninterruptedly using magnetic flux of permanent magnets to increase the induced voltage and by minimizing the phase difference between an induced voltage vector and a generated voltage vector, and to efficiently take out DC power from power of blades by suppressing the winding impedance to a low level. In order to increase the amount of power generated at start-up, it is required to reduce cogging torque and friction torque, and also to reduce iron losses such as a hysteresis loss and an eddy-current loss.
Japanese Patent Application Publication No. 2002-153036 (FIG. 1) discloses an axial-gap generator. This axial-gap generator is of a conventional type and employs a coreless structure having no iron core at the center of a winding. Permanent magnets are disposed on both sides of the winding to interpose the winding. Such a coreless winding structure allows reducing the winding impedance and the iron losses. However, magnetic flux of the permanent magnets is decreased in such a coreless winding structure. Therefore, the permanent magnets are disposed as discussed above to increase magnetic flux.
The structure according to Japanese Patent Application Publication No. 2002-153036 has a number of disadvantages as follows: few heat transfer paths for heat produced by the winding, which likely raises the winding temperature; a narrow gap between the winding and the permanent magnets, which makes it difficult to adjust the gap in assembling the generator; if the winding is molded with a resin, the risk of contact between the permanent magnets and the resin which has thermally been expanded due to the increased temperature of the winding; significantly increased material costs due to a large number of permanent magnets used: and a large inertia moment of the rotor, which increases start-up torque and reduces power generation.